Process and apparatus of co2 energy source adopted in solid oxide fuel cell - co2 energy conversion cycle

ABSTRACT

A process and apparatus of “Solid Oxide Fuel Cell (SOFC)-CO 2  Energy Conversion Cycle (referred to as SOFC-CO 2 -ECC)” are invented to adopt CO 2  as energy sources from waste/stock gas or convert and fix it in the useful compounds. CO 2  is converted into CO and O 2  via simultaneously catalytic and electrochemical reactions in SOFC for power generation and CO 2  cracking. Furthermore, CO is used either as the fuel in SOFC for power generation or starting materials in the chemical reactors to produce CO-derivatives of energy source materials and useful chemical compounds. Hence, SOFC-CO 2 -ECC is an active or scientific carbon cycle with zero emission of CO 2 . Thus, the efficacy of environmental protection via solving the problem of CO 2  greenhouse effect is achieved, so as to grasp of the “Right of Carbon Emission Trading” issues.

CROSS-REFERENCE TO RELATED APPLICATIONS

This non-provisional application claims priority under 35 U.S.C. §119(a)on Patent Application No(s). 099138558 filed in Taiwan, R.O.C. on Nov.9, 2010, the entire contents of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a process and apparatus of CO₂ energysource adopted in SOFC-CO₂-ECC, in which CO₂ is adopted as oxidantsource for power generation. An innovative solution is provided, tosolve greenhouse effect issue caused by increasing CO₂ concentration inthe atmosphere. Due to simultaneously high-temperature (700-1000° C.)catalytic and electrochemical reactions in the SOFC, CO₂, a compoundhaving extreme chemical stability, is cracked at about 800° C. followinga chemical reaction below: CO₂→CO_((g))+½O₂, to generate CO_((g)) andO₂, then O₂ electrochemically reacts with H₂ (or other hydrocarbons,such as methane) in the SOFC for power generation. As such, CO₂ mayserve as a power source material in an overall reaction of the SOFC, andconverted into a very useful energy source or compound CO, which can bederived into useful compounds or energy source, for example, aldehydesand alcohols, for regeneration of energy source, so as to complete anoverall energy conversion carbon cycle of CO₂→CO→derivatives of CO(fixation of CO₂)→generation of energy source→CO₂, and achieve zeroemission of CO₂. Technical solutions, auxiliary materials and equipmentsof the present invention are capable of effectively solving the problemof global extinction of organisms caused by greenhouse effect of CO₂.

2. Related Art

The development of human civilization mainly relies on the developmentof the materials and technologies using energy sources. Amonghydrocarbon oxides, coal and petroleum are extensively used due to theadvantage of dual purposes of fixed position and mobility, and productsafter use of coal and petroleum are mainly oxides such as CO₂ and H₂O,or NOx, SOx, and COx, which are all air pollution gases except H₂O.Furthermore, CO₂ has high output and is a stable compound, and is onlyconverted and consumed through plant photosynthesis, and thus beingpersistently remained in the atmosphere. Although CO₂ may be preparedinto dry ice and serve as gas for secondary enhancement of oil recoveryfor an oil well, it has few uses. Long-term high output of CO₂ leads tosharp increase of CO₂ level in the air, and triggers greenhouse effect,global warming, frequent natural disasters, and abnormal climate, andthe problem has reached the degree of no time to delay. However, the“energy saving and carbon reduction policy” involves the use of nuclearenergy and forest conservation and forestation, and also involvesreduction of use of petroleum and coal fuels However, the currentcivilization improvement and economic development have to rely on supplyof energy sources. In addition to compromise of the two aspects, it isnecessary to find a new solution of CO₂ problem.

Due to international extensive consumption and use of fossil energysources, the amount of the product CO₂ is continuously increased, andthe whole atmosphere of the earth is polluted, and thus resulting ingreenhouse effect and threats and risks to living conditions of humanbeing and other related organism on the earth. It is estimated that CO₂content in the atmosphere is continuously exponentially increased to 380ppm in 2000, and the annual increase rate is gradually accelerated,which may be attributed to man's increasing combustion of fossil fuels.Therefore, the issue of “energy saving and carbon reduction” is raised,to rescue the earth and solve the problem of human survival. In thisissue, various processes are set forth to provide a solution for the CO₂problems. It is emphasized in Copenhagen conference (COP-15) that inorder to combat global climate change, global carbon emission must bereduced greatly, to control the global temperature rise to be below 2°C. and the global average CO₂ concentration in 2050 to be returned to450 ppm, because among greenhouse gases (water vapor=36-70%; carbondioxide=9-26%; methane=9%; ozone=3-7%), CO₂ is the main cause.

At present, solution of this issue in world is directed to developmentof the technologies of CO₂ capture, storage and, reutilization. It isexpected to effectively lower CO₂ content in the atmosphere and solvethe greenhouse issue through fixed storage or by fixing CO₂ through achemical reaction, such as CO₂+CaO, to generate a solid such as CaCO₃,so as to extract large volume of CO₂(g) from the atmosphere forsolidification.

For the CO₂ cracking chemical reaction CO₂(g)→CO(g)+½O₂(g), aspontaneous reaction temperature is 3001.5° C. according tothermodynamic calculation, and thus the reaction cannot be effectivelyovercome and implemented by using the current useful technology andapparatus. Therefore, CO₂ greenhouse gas cannot be solved, and becominga problem around the world.

SOFCs have advantages of high energy conversion efficiency, low noise,low environment pollution, high reliability, and diversity of fuel, andhave the potential of challenging “internal-combustion engine”, and thusbeing capable of solving the problem of energy shortage in future.Especially, the fossil energy sources are gradually depleted, andreplaced by gasified and liquefied coal sources, and thus coal fuel eracomes, in which SOFCs are the apparatus of main energy source converterand will play an innovative role in the era. With the successful ofperformance stability and long-term operation test of SOFCs, technologyand functions of apparatus become mature gradually. In the future,distributed or centralized power generators or power plants willgradually replace the existing coal-fired power plants, and thus theeconomic benefits are very large.

Presently, in an SOFC, H₂, natural gas, or a fossil fuel (for example,hydrocarbons such as methane, alcohols, alkanes or alkynes, or evendiesel) is fed into an anode as fuel, and O₂ in air is fed into acathode as oxidant, and the chemical energy is directly converted intoelectric energy via simultaneously or sequentially electrochemical andcatalytic chemical reactions. Main products at the anode are CO₂ andH₂O, and O₂ depleted air at the cathode. Therefore, main cause CO₂ ofgreenhouse effect is naturally generated. However, as the energy sourceconversion rate (up to 70-80%) of the SOFC is much higher than that of aconventional coal-fired power plant (generally about 20-30%), for acertain amount of fuel, the SOFC can achieve a function of energyincrease and carbon reduction. This advantage can only lower theemission of CO₂, and thus partly achieving the purpose of energy savingand carbon reduction.

At present, solving of the problem of greenhouse effect in world isdirected to development of technologies of CO₂ capture, storage, andreutilization. However, the development is still at an initial stage,and no specific and effective method is set forth for solving theproblem. One process or procedure is provided, in which CO₂ is fixed andstored, or converted into a solid through a chemical reaction, such asCO₂+CaO→CaCO₃, so as to extract large volume of CO₂(g) from theatmosphere for solidification, thereby effectively lowering the CO₂content in the atmosphere. Furthermore, a primitive process in thenature is to plant a lot of forests and seaweed plants, such thatchlorophyll photo-synthesis is performed, to convert CO₂ into plantingredients, thereby lowering the CO₂ content in the atmosphere. Boththe processes are feasible but contradict the increase tendency inenergy source demand, have many difficulties, are passive solutions andactions, and belong to natural carbon cycle.

According to the process and the apparatus of CO₂ energy source adoptedin SOFC-CO₂-ECC of the present invention, waste CO₂, main cause ofgreenhouse effect, is converted into energy source materials by an SOFC,by cracking CO₂ as SOFC cathode oxidant, in presence of SOFC anode fuelsuch as H₂ following CO₂→CO_((g))+½O₂, CO is generated for powergeneration. CO is a high-activity compound, and may be used as fuel ofthe SOFC (in SOFC anode) for power generation with O₂ in air at thecathode, to generate electric energy and CO₂, thereby “use-regeneration”and power generation ECC of CO₂ is completed. Furthermore, CO may reactwith H₂ and O₂ to synthesize a stable compound, such as useful solid orliquid compounds of alcohols, aldehydes, and acids, and thus beingsafely stored in the earth for recycle and reutilization. As a result,the CO₂ content in the atmosphere is lowered, and the problem ofgreenhouse effect is solved. The process and the apparatus of thepresent invention are an active process for solving the CO₂ problem.

SUMMARY OF THE INVENTION

The present invention is directed to a process and an apparatus of CO₂energy source adopted in the solid oxide fuel cell—CO₂ energy conversioncycle (SOFC-CO₂-ECC). Main cause of greenhouse effect, waste CO_(2(g))is adopted as cathode oxidant of an SOFC and is cracked into CO_((g))and ½O₂, and the generated O₂ receives electrons and is conducted from acathode to an anode through an electrolyte and electrochemically reactsin the SOFC with an anode fuel such as H₂, CH₄, alkanes, andhydrocarbons for power generation and thus depleted, which mayeffectively promote the conversion of waste CO₂ into CO, such that CO₂is further fixed in a useful solid or liquid compound. In the presentinvention, in a general chemical reaction (in the presence of acatalyst), CO₂→CO_((g))+½O₂ cannot be carried out because the feasibleor spontaneous reaction temperature is 3001.5° C. or above according tothermodynamic calculation. However, in the process and the apparatus ofCO₂ energy source adopted in SOFC-CO₂-ECC of the present invention, thespontaneous reaction may be carried out at about 800° C. viasimultaneously catalytic and electrochemical reactions in the SOFC. Thisjust meets a current medium-to-high operating temperature in an SOFC of700-1000° C. In this way, a problem that CO₂ cannot be converted due toextreme stability is solved, and CO₂ is converted into CO_((g)) which iseasy to handle and may be used as anode fuel of the SOFC and react withO₂ in cathode air for power generation. Furthermore, general chemicalreactions with other compounds containing carbon, hydrogen, or oxygenmay be carried out with CO_((g)) as raw material, to prepare a derivedsolid or liquid compound, for example, alcohols such as CH₃OH, acids, oraldehydes, and other reaction products, for being stored or recycled invarious products and industries.

In an embodiment, the present invention provides a process of CO₂ energysource adopted in SOFC-CO₂-ECC, which includes:

providing an apparatus of CO₂ energy source adopted in SOFC-CO₂-ECC;

introducing hydrogen to an anode of a first SOFC, and introducing CO₂ toa cathode of the first SOFC, such that catalytic and electrochemicalreactions occur in the first SOFC, to generate CO and H₂O;

introducing air to a cathode of a second SOFC, and introducing COgenerated at the cathode of the first SOFC to an anode of the secondSOFC; and

feeding CO₂ generated at the anode of the second SOFC back into thecathode of the first SOFC.

In another embodiment, the present invention provides an apparatus ofCO₂ energy source adopted in SOFC-CO₂ ECC, which includes a first SOFCand a second SOFC.

In the first SOFC, hydrogen is introduced to an anode, and CO₂ isintroduced to a cathode, CO₂ is finally cracked into CO and H₂O, mainchemical reactions at the anode includes H₂(g)→H₂ (anode)→2H⁺(anode)+2e− and 2H⁺ (anode)+O²⁻ (anode)→H₂O(g), or an overall chemicalreaction at the anode is H₂(g)+O²⁻ (anode)→H₂O(g)+2e−; main chemicalreactions at the cathode include CO₂(g)→CO₂ (cathode)→CO (cathode)+½O₂(cathode), CO (cathode)→CO(g) and ½O₂ (cathode)+2e−→O²⁻ (cathode); amain chemical reaction in an electrolyte is oxygen ion conduction: O²⁻(cathode)→O²⁻ (anode); and an overall chemical reaction in the firstSOFC is H₂(g)+CO₂(g)→H₂O(g)+CO(g).

The second SOFC is connected in series to the first SOFC, in which COgenerated after CO₂ is cracked in the first SOFC is introduced to ananode of the second SOFC and air is introduced to an cathode for powergeneration, and CO₂ generated after power generation in the second SOFCis further introduced to the cathode of the first SOFC, main chemicalreactions at the anode include CO(g)→CO (anode) and O²⁻ (anode)+CO(anode)→CO₂ (anode)+2e−; a main chemical reaction at the cathodeincludes ½O₂(g)→½O₂(cathode)+2e−→O²⁻ (cathode); a main chemical reactionin an electrolyte is oxygen ion conduction: O²⁻ (cathode)→O²⁻ (anode);and an overall chemical reaction in the second SOFC 11 isCO(g)+½O₂(g)→CO₂(g).

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given herein below for illustration only, and thusare not limitative of the present invention, and wherein:

FIG. 1A is a schematic view of an apparatus of CO₂ energy source adoptedin SOFC-CO₂ ECC;

FIG. 1B is a schematic view of an apparatus of CO₂ energy source adoptedin SOFC-CO₂ ECC including a CO stripper;

FIG. 2 is a flow chart of a process of CO₂ energy source adopted inSOFC-CO₂-ECC;

FIG. 3 is a flow chart of an experiment of an effect of a first SOFC;

FIG. 4 is a schematic view of compartment of a cathode chamber and ananode reaction chamber of a SOFC-MEA;

FIG. 5 is an electrical test diagram of a first SOFC with hydrogen andair respectively at an anode and a cathode,

FIG. 6 is an electrical test diagram of a first SOFC with hydrogen andCO₂ respectively at an anode and a cathode;

FIG. 7A-7D are a result diagram of CO₂ conversion yield tested with atest system at different operation temperatures with H₂/N₂ and CO₂ at ananode and a cathode respectively;

Table A shows test data of a first solid oxide fuel cell; and

Table B shows results of CO₂ conversion yield.

DETAILED DESCRIPTION OF THE INVENTION

The technical means for achieving the objectives of the presentinvention and effects thereof are described below with reference toaccompanying drawings; however, the embodiments recited in the drawingsbelow are provided for illustration and for the Examiner to understandthe present invention, and the technical means of the present inventionis not limited to the recited drawings.

FIG. 1A is a schematic view of an apparatus of CO₂ energy source adoptedin SOFC-CO₂ ECC, which includes a first SOFC 10 and a second SOFC 11.

In the first SOFC 10, hydrogen is introduced to an anode, and CO₂ isintroduced to a cathode, CO₂ is finally cracked into CO and H₂O, inwhich main chemical reactions at the anode include H₂(g)→H₂ (anode)→2H⁺(anode)+2e− and 2H⁺ (anode)+O²⁻ (anode)→H₂O(g), or an overall chemicalreaction at the anode is H₂(g)+O²⁻ (anode)→H₂O(g)+2e−; main chemicalreactions at the cathode include CO₂(g)→CO₂ (cathode)→CO (cathode)+½O₂(cathode), CO (cathode)→CO(g) and ½O₂ (cathode)+2e−→O²⁻ (cathode); amain chemical reaction in an electrolyte is oxygen ion conduction: O²⁻(cathode)→O²⁻ (anode); and an overall chemical reaction in the firstSOFC 10 is H₂(g)+CO₂(g)→H₂O(g)+CO(g).

The second SOFC 11 is connected in series to the first SOFC, in which COgenerated after CO₂ is cracked in the first SOFC 10 is introduced to ananode of the second SOFC 11 and air is introduced to an cathode forpower generation, and CO₂ generated after power generation in the secondSOFC 11 is further fed to the cathode of the first SOFC 10, mainchemical reactions at the anode include CO(g)→CO (anode) and O²⁻(anode)+CO (anode)→CO₂ (anode)+2e−, in which in order to eliminate thedamage on the cell caused by carbon deposition on the anode, a suitablequantity of H₂, gaseous H₂O, or a mixture thereof may be co-fed with CO,to improve the material and structure of the anode at the same time,that is, to solve carbon deposition problem of Doudouard reaction; amain chemical reaction at the cathode includes½O₂(g)→½O₂(cathode)+2e−→O²⁻ (cathode); a main chemical reaction in anelectrolyte is oxygen ion conduction: O²⁻ (cathode)→O²⁻ (anode); and anoverall chemical reaction in the second SOFC 11 is CO(g)+½O₂(g)→CO₂(g).

As shown in FIG. 1B, the apparatus of CO₂ energy source adopted inSOFC-CO₂-ECC may further include a CO stripper 13 for separating CO fromCO₂ to improve the concentration of CO, which has one end connected to avent of the cathode of the first SOFC 10, and an other end split intothree pipelines connected to the anode of the second SOFC 11, a gasinlet of the cathode of the first SOFC 10, and a chemical reactor 12respectively, and one of the three pipelines is selected fortransporting the gas according to the concentration of CO aftertreatment, for example, high concentration of stripped CO is fed intothe chemical reactor 12, to react with hydrogen, oxygen, or a mixturethereof, so as to convert CO into a liquid or solid compound forstorage. Or, CO is fed into the anode of the second SOFC 11 for powergeneration.

The first SOFC 10 may be a tubular type or a planar type, the cell maybe an anode support cell (ASC) type, an electrolyte support cell (ESC)type, or a metal support cell (MSC) type, and the cell structure is aNiO—YSZ type, an YSZ type, or an LSM−GDC+LSM type, in which NiO—YSZ isan anode, YSZ is an electrolyte layer, and LSM−GDC+LSM is a compositecathode layer, but the present is not limited to the above types andmaterials.

The second SOFC 11 may be a tubular type or a planar type, the cell isan ASC type, an ESC type, or an MSC type, and the cell structure is aNiO—YSZ type, an YSZ type, or an LSM−GDC+LSM type, in which NiO—YSZ isan anode, YSZ is an electrolyte layer, LSM−GDC+LSM is a compositecathode layer, and the anode is treated with CeO₂—Cu, but the present isnot limited to the above types and materials, and the anode may betreated with CeO₂—Cu, to combat carbon deposition.

The reaction temperature in the first SOFC 10 is about 700-1000° C., theelectrolyte is preferably YSZ or ScSZ, a catalyst having a highcatalytic activity such as platinum (Pt) or a noble metal may be dopedin the cathode to improve the conversion yield.

The reaction temperature in the second SOFC is about 600-1000° C.

FIG. 2 is a flow chart of a process of CO₂ energy source adopted inSOFC-CO₂-ECC, and the process includes the following steps.

Step 20 is performed firstly, in which an apparatus of CO₂ energy sourceadopted in SOFC-CO₂-ECC is provided.

Then, Step 21 is performed, in which hydrogen is introduced to the anodeof the first SOFC 10, and CO₂ is introduced to the cathode of the firstSOFC 10, such that catalytic and electrochemical reactions occur in thefirst SOFC 10, to generate CO and H₂O.

Next, Step 22 is performed, in which air is introduced to the cathode ofthe second SOFC 11, and CO generated at the cathode of the first SOFC 10is introduced to the anode of the second SOFC 11, in which in order toavoid the problem of carbon deposition, a suitable quantity of H₂,gaseous H₂O, or a mixture thereof may be added when CO is introduced tothe anode of the second SOFC 11.

Finally, Step 23 is performed, in which CO₂ generated at the anode ofthe second SOFC 11 is fed back into the cathode of the first SOFC 10.

After Step 21, a step of separating CO from CO₂ to improve theconcentration of CO and introducing the high concentration of CO intothe chemical reactor 12 for reacting with hydrogen, or oxygen, or amixture thereof to convert CO into a liquid or solid compound forstorage is further included.

FIG. 3 is a flow chart of an experiment of an effect of the first SOFC.In this experiment, an ASC is used, the cell has a structure of an anodeof NiO/8YSZ, an electrolyte of YSZ, and a cathode of LSM+GDC/LSM, andthe experiment includes the following steps.

Step 30 is performed firstly, in which an SOFC-Membrane ElectrodeAssembly (MEA) is set at a cell test station (for example, ProboStatUnit) and platinum wires are respectively attached to a cathode and ananode of the MEA. A golden ring is melted at about 1053° C. and seals acathode of MEA or cell and an alumina tube end of the cell test station,to isolate a cathode reaction chamber and a anode reaction chamber to angas tight grade. The schematic structural view of the apparatus and thecell chambers is as shown in FIG. 4. The platinum wires of the cathodeand the anode are respectively attached to, for example, aProboStat-[solartron-SI-1287 (Electrochemical Interface)/1267(Impedance/Gain-Phase Analyzer] system, for cell performance datacollection, including potential/current/power density (V-I-P) vs. timerelation and temperature-related data recording.

Then, Step 31 is performed, in which the cell test station is set in ahigh-temperature oven, and heated (for example, ProboStat) to 1053° C.at a temperature raising rate of 1° C./min (generally lower than 3°C./min), while N₂ is introduced to the anode to serve as a leakagetesting gas when the cathode reaction chamber and the anode reactionchambers are sealed with the golden ring, till it is confirmed that thereaction chambers at the cathode end and the anode end of the MEA areisolated, and no transfer and leakage of gas occur.

Next, Step 32 is performed, in which H₂ is introduced to the anode toreduce anode NiO to Ni, and air is introduced to the cathode at the sametime. It is tested whether an open circuit voltage (OCV) reaches 1.0V orabove (at 800° C.), to confirm whether the structure of the MEA (cell)is qualified. Moreover, the V-I-P and the electrical impedance spectrum(EIS) of the test cell are persistently recorded, to confirm themagnitude of electricity, so as to determine whether the cell and thewires are in good contact. Therefore, at an earlier stage of performancetest of the MEA, H₂ (anode)/air (cathode) are used as system gas, toverify whether the cell and the system is in good state. The testresults are as shown in FIG. 5.

Subsequently, Step 33 is performed, in which the gas introduced to theanode is kept unchanged, the gas introduced to the cathode is CO₂instead, and the OCV and the V-I-P, and composition and concentration ofreaction products (CO₂/CO/O₂) at the cathode are tested and recordedrespectively at 840° C., 890° C. and 938° C. It is confirmed that CO₂may be used as cathode oxidant gas of the first SOFC, suggesting thatCO₂(g)→CO(g)+½O₂(g) is feasible to be performed at the cathode, and O₂may be successfully provided in progression of electrochemical reactionand be used for current generation. Experimental results are as shown inFIGS. 6, 7A, 7B, 7C, 7D, and Tables A and B, and the correctness of thesystem and the feasibility of SOFC-CO₂-ECC are confirmed. COconcentration may be up to 27.83 mol % (that is, conversion ofCO₂=0.2783), and O₂ concentration is 0% in one reaction pass, indicatingthat O₂ generated in cracking of CO₂ is completely depleted at thecathode.

Afterwards, Step 34 is performed, in which after the cell performancetest is completed, the gas flow rate is lowered, the anode is maintainedin a reduction atmosphere, and cooled to room temperature at atemperature drop rate of 1° C./min (generally lower than 3° C./min), andthen the fed gases are completely closed. Thus, the main test of thesystem is completed.

Finally, Step 35 is performed, in which the cell performance data isanalyzed to identify the feasible achievement of the SOFC-CO₂-ECC. It isverified through this test result that the present invention is capableof effectively treating the main cause of the greenhouse gas CO₂ bycycling CO₂ for use in the second SOFC for power generation on one hand,and by cracking CO₂ into CO having high activity on other hand, whichcan react with other substance such as hydrogen or oxygen to generate auseful solid or liquid compound, such that CO₂ in the atmosphere isconverted into a solid or liquid compound, thereby achieving the purposeof energy saving and carbon reduction, so as to eliminate CO₂ greenhousegas.

FIGS. 7A, 7B, 7C, and 7D are result diagrams of CO₂ conversion yieldtested with a test system respectively at an anode and a cathode withH₂, N₂ and CO₂ at different operation temperatures, and test resultdiagrams of concentrations of reactant CO₂ and product CO vs operationpotential at different operation temperatures, in which temperatures inFIGS. 7A, 7B, and 7C are respectively 840° C., 890° C., and 938° C.; andFIG. 7D is a test result diagram of concentrations of reactant CO₂ andproduct CO vs flow rate of reactants at an operation temperature of 938°C.

Although the preferred embodiments of the present invention aredescribed in detail above, they are not intended to limit the scope ofthe present invention. Any equivalent variations or modifications madewithout departing from the spirit of the present invention shall fallwithin the scope of the present invention.

1. An apparatus of CO₂ energy source adopted in Solid Oxide Fuel Cell(SOFC)-CO₂ energy conversion cycle (SOFC-CO₂-ECC), comprising: a firstSOFC, wherein hydrogen is introduced to an anode, CO₂ is introduced to acathode, CO₂ is finally cracked into CO and H₂O, main chemical reactionsat the anode comprises: H₂(g)→H₂ (anode)→2H⁺ (anode)+2e− and 2H⁺(anode)+O²⁻ (anode)→H₂O(g), or an overall chemical reaction at the anodeis H₂(g)+O²⁻ (anode)→H₂O(g)+2e−; main chemical reactions at the cathodecomprises CO₂(g)→CO₂ (cathode)→CO (cathode)+½O₂ (cathode), CO(cathode)→CO(g) and ½O₂ (cathode)+2e−→0²⁻ (cathode); a main chemicalreaction in an electrolyte is oxygen ion conduction: O²⁻ (cathode)→O²⁻(anode); and an overall chemical reaction in the first SOFC isH₂(g)+CO₂(g)→H₂O(g)+CO(g); and a second SOFC, connected in series to thefirst SOFC, wherein CO generated after CO₂ is cracked in the first SOFCis introduced to an anode of the second SOFC, CO₂ generated after powergeneration in the second SOFC is introduced into the cathode of thefirst SOFC, main chemical reactions at the anode comprise CO(g)→CO(anode) and O²⁻ (anode)+CO (anode)→CO₂ (anode)+2e−; a main chemicalreaction at a cathode is ½O₂(g)→½O₂ (cathode)+2e−→O²⁻ (cathode); a mainchemical reaction in an electrolyte is oxygen ion conduction: O²⁻(cathode)→O²⁻ (anode); and an overall chemical reaction in the secondSOFC is CO(g)+½O₂(g)→CO₂(g).
 2. The apparatus of CO₂ energy sourceadopted in SOFC-CO₂-ECC according to claim 1, further comprising a COstripper for separating CO from CO₂, having one end connected to a ventof the cathode of the first SOFC, and an other end split into threepipelines connected to the anode of the second SOFC, a gas inlet of thecathode of the first SOFC, and a chemical reactor respectively, whereinin the chemical reactor, the introduced CO reacts with hydrogen, oxygen,or a mixture thereof, to generate a useful liquid or solid compound. 3.The apparatus of CO₂ energy source adopted in SOFC-CO₂-ECC according toclaim 2, wherein the first SOFC is a tubular type or a planar type, thecell is an anode support cell (ASC) type, an electrolyte support cell(ESC) type, or a metal support cell (MSC) type, a cell structure is aNiO—YSZ type, a YSZ type, or an LSM−GDC+LSM type, NiO—YSZ is an anode,YSZ is an electrolyte layer, and LSM−GDC+LSM is a composite cathodelayer.
 4. The apparatus of CO₂ energy source adopted in SOFC-CO₂ ECCaccording to claim 2, wherein the second SOFC is a tubular type or aplanar type, the cell is an anode support cell (ASC) type, anelectrolyte support cell (ESC) type, or a metal support cell (MSC) type,a cell structure is a NiO—YSZ type, a YSZ type, or an LSM−GDC+LSM type,NiO—YSZ is an anode, YSZ is an electrolyte layer, LSM−GDC+LSM is acomposite cathode layer, and the anode is treated with CeO₂—Cu.
 5. Theapparatus of CO₂ energy source adopted in SOFC-CO₂-ECC according toclaim 2, wherein a reaction temperature in the first SOFC is about700-1000° C.
 6. The apparatus of CO₂ energy source adopted inSOFC-CO₂-ECC according to claim 2, wherein a reaction temperature in thesecond SOFC is about 600-1000° C.
 7. The apparatus of CO₂ energy sourceadopted in SOFC-CO₂-ECC according to claim 2, wherein a noble metal isadded in the first SOFC as catalyst.
 8. The apparatus of CO₂ energysource adopted in SOFC-CO₂-ECC according to claim 7, wherein the noblemetal is platinum.
 9. A process of CO₂ energy source adopted in SolidOxide Fuel Cell (SOFC)-CO₂ Energy Conversion Cycle (SOFC-CO₂-ECC),comprising: providing an apparatus of CO₂ energy source adopted inSOFC-CO₂-ECC; introducing hydrogen to an anode of a first SOFC, andintroducing CO₂ to a cathode of the first SOFC, such that catalytic andelectrochemical reactions occur in the first SOFC, to generate CO andH₂O; introducing air to a cathode of a second SOFC, and introducing COgenerated at the cathode of the first SOFC to an anode of the secondSOFC; and feeding CO₂ generated at the anode of the second SOFC backinto the cathode of the first SOFC.
 10. The process of CO₂ energy sourceadopted in SOFC-CO₂-ECC according to claim 9, further comprisingseparating CO from CO₂, to improve a concentration of CO, and feedingthe concentrated CO into a chemical reactor, to react with hydrogen,oxygen, or a mixture thereof, so as to convert CO into a useful liquidor solid compound for storage.
 11. The process of CO₂ energy sourceadopted in SOFC-CO₂-ECC according to claim 9, wherein a suitablequantity of H₂, gaseous H₂O, or a mixture thereof is added when COgenerated at the cathode of the first SOFC is introduced to the anode ofthe second SOFC.